Phage head assembly: During bacteriophage capsid morphogenesis, the procapsid (prohead) is assembled with the aid of which helper proteins?

Introduction / Context:
Assembly of icosahedral bacteriophage heads proceeds through a precursor called the procapsid (or prohead). This intermediate relies on transient helper proteins that guide correct geometry before DNA packaging and maturation. Knowing these helper proteins by name and function is foundational for phage assembly questions.

Given Data / Assumptions:

• Procapsid forms prior to genome packaging.
• Helper proteins are not part of the final mature capsid.
• Only one response corresponds to standard terminology.

Concept / Approach:
“Scaffolding proteins” bind coat protein subunits during early assembly, enforcing correct angular relationships. After capsid maturation (often accompanied by proteolysis and expansion), scaffolding components are released or degraded, leaving a stable head shell ready for DNA packaging.

Step-by-Step Solution:
Identify the stage: procapsid formation precedes DNA packaging. Recall helper terminology: scaffolding proteins template geometry. Exclude terms not used in phage literature (ladder, framing, form). Select “Scaffolding proteins.”

Verification / Alternative check:
Classical models from phages like P22 and T7 document scaffolding proteins that are removed upon maturation, validating their transient role.

Why Other Options Are Wrong:
“Ladder,” “framing,” and “form” are not standard phage assembly terms; chaperonins assist general folding but do not define the procapsid templating function.

Common Pitfalls:
Assuming helper proteins remain permanently in the capsid; in most systems, they are removed during maturation.

Final Answer:
Scaffolding proteins.